The general hypothesis that injury of pulmonary vascular endothelium involves direct responses of the endothelial cells themselves to toxic stimuli will be tested using endothelial cells grown in culture and explants of pulmonary artery intima. The endothelial responses may include intracellular generation of toxic oxygen radicals and generation of metabolites of arachidonic acid. These products may both alter the endothelial layer and affect its interaction with inflammatory cells. Activation of complement may also affect both the direct response of the endothelial cells to injurious stimuli and their interactions with inflammatory cells. Finally, inflammatory cells, per se, may potentiate the endothelial injury. To test the hypothesis, the barrier function of the endothelial layer of pulmonary artery intima and endothelial monolayers grown in culture will be measured by equilibration of isotopic tracers across the membrane and by direct measurement of hydraulic conductance. The effects of interventions on the structure of endothelial cells in both preparations will be followed and production of both lipoxygenase and cyclooxygenase products of arachidonic acid by endothelium over the course of the induced injury will be evaluated. The direct effects of various eicosanoids on endothelial structure, metabolism and function will be determined as will the question of whether an exogenous source of arachidonic acid causes the otherwise benign process of transendothelial migration of granulocytes to injure the endothelium. Measurements will be made of the effects of endotoxin and purified lipid-A on endothelial structure, metabolism and function. Measurements will also be made to determine how endotoxin alters the interactions of endothelium with leukocytes, to determine whether antioxidant enzymes delivered into cells by liposome encapsulation alter the endothelial response to endotoxin and to determine whether corticosteroids, nonsteroidal antiinflammatory drugs and free radical scavengers affect the endotoxin-induced injury. Susceptibility of different lines of cultured endothelial cells from several species to endotoxin will be examined and the role of complement in endotoxin-induced endothelial injury in the presence and absence of leukocytes will be studied. The proposed studies result from an extensive base of structural and functional information obtained in whole animal preparations and from a large amount of preliminary data suggesting that the goals of the studies are feasible. The studies will provide new information about cellular and humoral mechanisms of pulmonary vascular injury and provide a rationale for innovative approaches for prevention and therapy of diffuse lung injury.